1. Field of the Invention
The present invention relates to a camera having a zoom function in which a focal length can be varied or the variation is actuated by a focal length changing member, and in particular to a camera in which a focal length is varied through a motor.
The present invention also relates to a motor driven zoom lens camera having an image magnification selection mode, and also to a camera having a zoom clip mode in which a zoom lens is moved to a predetermined focal length.
2. Description of Related Art
A known zoom lens camera has a zoom ring as a focal length changing member, which can be rotated to vary the focal length. Also known is a camera having an automatic focusing function (AF function) in which an image of an object to be taken is automatically focused. In such a known AF camera having a zooming function, the AF function is performed when a shutter button is depressed halfway and a photometering switch is made ON.
Consequently, in the known camera, if a photographer attempts to change the framing by rotating the zoom ring to vary the focal length and at the same time observes an object through a view finder, unless the shutter button is halfway, no AF function takes place so that a dimmed object image is seen in the view finder.
After effecting automatic focusing by pressing the shutter button halfway, the photographer fully presses the shutter button to actuate a release switch to thereby take a picture. A small or narrow focusing range is set so that a precise focusing can be realized. However, with a particularly small focusing range, if the focusing is carried out during zooming, it can take a long time before a precise focusing operation is completed or alternatively fine focusing adjustments are repeatedly effected so long as no object image is in focus. This can be disquieting to a photographer.
A recently developed and marketed zoom lens camera has a motor driven zoom lens in which the focal length is varied by a zoom motor. With such a camera, an image magnification (image size) of an object to be taken can be easily maintained constant whereas in conventional cameras having no motor-driven zoom function, image magnification has required a high level of photographing technique. To this end, it is necessary to set a desired image magnification in the camera body.
The image magnification referred to is determined based on the object distance and the current focal length. The object distance is determined in accordance with the position of the zoom lens which is moved during the focusing operation. Consequently, the image magnification can be set only after the focusing operation is completed.
As already noted, the focusing operation is carried out when a shutter button is depressed halfway to actuate a photometering switch. Therefore, upon setting an image magnification, it is necessary for a photographer to use one hand to actuate a zoom ring to obtain a desired focal length whilst using the other hand to press the shutter button down halfway. This results in a troublesome operation.
In the above described camera having a motor driven zoom lens, it is easy to effect a so-called zoom operation in which the zoom motor is automatically moved to a predetermined focal length, for example, by pressing a zoom set button. However, as is known from the conventional AF zoom lens camera, the focusing operation takes place when a shutter button is pressed down halfway to actuate a photometering switch.
Therefore, if a photographer attempts to effect zoom clipping operation while observing an object image through a view finder, the shutter button needs to be pressed to obtain the AF function. Otherwise, the zoom clipped object image in the view finder is dimmed.
In the above described motor-driven zoom lens camera, it is also easy to effect zooming during exposure (referred to as an in-exposure zooming) so that the focal length is varied in the course of the exposure operation, whereas in conventional cameras having no motor driven zoom function, this has required a high level of photographing technique.
However, the direction of the in-exposure zooming in the known motor driven zoom lens camera is predetermined. Thus, if the zooming direction is predetermined to be for a telephoto direction, in the event that the detected current focal length is at a telephoto extremity, no zooming can be practically effected. Consequently, even if an in-exposure zooming mode has been set, no in-exposure zooming is practically carried out. Thus, there has been a long felt need for solving this problem.
In the known motor driven zoom lens camera for in-exposure zooming, the zooming speed, and the zooming direction, etc., are predetermined on the camera body side so that the in-exposure zooming takes place in accordance with predetermined conditions in the course of an automatic power zooming operation. Thus, a photographer can easily effect in-exposure zooming in accordance with the conditions preset in the camera body. However, if the photographer tries to effect in-exposure zooming in accordance with conditions different from those preset in the camera body, for example with a desired zooming speed or zooming direction, etc., the preset data must be changed in advance, which is troublesome. There has been a long felt need for an improvement.
As already noted, in the known motor driven zoom lens camera for in-exposure zooming, the zooming speed is predetermined in the camera body. Accordingly, for example, if the zooming speed is set high in spite of a low shutter speed, there can be two image cores from the in-exposure zooming, i.e., an image core before the completion of the zooming and an image core after the completion of the zooming. Thus, a defective picture results.
With the in-exposure zooming in known motor driven zoom lens cameras, once the shutter speed is set to the bulb mode (i.e., in an open position), a photographer cannot tell the exposure time, and accordingly, it is impossible to automatically carry out the power zooming, for example, for a time equal to half the exposure time. Namely, once the shutter speed is set to the bulb setting no in-exposure zooming can be carried out with the conventional camera.